The present invention relates to a magnetic memory drive which can detect a tracking error signal stably with high precision, and which can record, reproduce or erase information accurately to or from a magnetic recording medium such as a hard magnetic disk or a flexible magnetic disk.
Previously, track positioning is carried out mechanically in a rough manner by using a stepping motor or the like because a magnetic disk system for recording information on a magnetic recording medium has a very wide track pitch of approximately 200 xcexcm as compared with that of an optical recording medium that is approximately 1.6 xcexcm. However, recently there have been an increasing demand for track pitches of several to a few tens micrometers in order to achieve a higher capacity. Then, the track positioning mechanism is required to be more accurate than the conventional mechanism.
In a conventional magnetic memory drive for detecting a tracking error signal optically, a laser diode light source emits a linearly polarized diverging beam, and a diffraction grating splits it into a plurality of beams. Then, the beam transmits through an objective lens to be condensed onto a magnetic recording disk. The beam is reflected by the disk to transmit through the objective lens and is split by the diffraction grating. A photodetector receives the beam, and it outputs an electric signal in accordance with a quantity of the received light. A signal processor processes the electric signal received from the photodetector and outputs a tracking error signal. Then, a driving section adjusts the position of the disk according to the tracking error signal. Then, a magnetic head records and reproduces information.
The diffraction grating has a first region formed on a face closer to the light source and a second region formed on another face on the opposite side. The beam emitted from the light source incident on the first region is split into three beams, that is, 0th-order and xc2x11st-order diffracted beams, and the three beams are further split into a plurality of beams by the second region. Only the 0th-order diffracted beam among the diffracted beams generated by the second region is incident on the aperture of the objective lens. Moreover, the beam, reflected by the disk, diffracted and being incident on the second region is split into a plurality of diffracted beams, and only the xc2x11st-order diffracted beams among them are received by the photodetector.
In a conventional magnetic memory drive, the ratio of quantities of lights of the three beams generated in the first region of the diffraction grating is appropriately set according to conditions on the machining property of the diffraction grating and on the design of the signal processor. Alternatively, an optical device fabricated as an integrated body of a light source, a diffraction grating and a photodetector is known as an element used for an optical disk drive which uses the three beam method, and it can be applied to a conventional magnetic memory drive under appropriate optical design conditions. Then, the optical device for optical disk is adopted from the viewpoint of cost reduction, but in this case, quantity of light Q0 of the 0th-order light beam and quantity of light Qxc2x11 of the xc2x11st-order light beams have a following ratio of Q0:Qxc2x11=5:1, according to its applicability to the optical disk.
For example, grating patterns formed in the first and second regions of the diffraction grating respectively have patterns of a constant pitch, and the grating pattern of the first region is perpendicular to that of the second region. The grating pitch of the first region is larger than that of the second region. The xc2x11st-order diffracted beams formed by the second region and received by the photodetector are respectively composed of three beams diffracted by the first region and three beams diffracted by the second region. The photodetector has six light receiving sections for the six beams. The six light-receiving sections of the photodetector 15 output electric signals corresponding to the quantities of received lights of the respective beams, and they are processed in a signal processor to output a tracking error signal. Upon receipt of the tracking error signal, a driver adjusts the relative position to disk 4. Consequently, a tracking operation to a desired track is carried out.
Here, in the conventional magnetic memory drive having the above-mentioned structure, the electric signals V5, V6 and V7, derived from the beam that has been reflected and diffracted by the disk and received by the photodetector, is determined on principle by only the displacement of the beam in the X-direction with respect to any one of the guide grooves, and it has nothing to do with the position of the guide groove on the disk. Therefore, it is supposed that the modulation degree and the maximum amplitude are always constant whether the position in question is located in the inner circumferential portion or in the outer circumferential portion on the disk. However, actually, in the conventional magnetic memory drive, the modulation degree and the maximum amplitude vary with the inner circumferential portion and the outer circumferential portion of the disk.
An object of the present invention is to provide a magnetic memory drive which can reduce tracking errors.
A magnetic memory drive according to the present invention comprises a light source which emitting a light beam, a diffraction grating which receives the beam emitted by the light source to generate three beams of 0th-order and xc2x11st-order light beams, a condensing system which converges the beams generated from the diffraction grating into a minute spot on a magnetic recording medium on which periodic physical variations are forced for providing variations in reflectivity, a photodetector which receives the beams reflected and diffracted from the magnetic recording medium and again passing through the condensing system and outputs signals corresponding to quantities of the received beams, a signal processor which processes the signals outputted from the photodetector to output a tracking error, a driver which receives the tracking-error signal outputted from the signal processor and positions the beams on a desired track, and a magnetic head which records information on the magnetic recording medium or reproduces or erases information on the magnetic recording medium. The photodetector comprises a plurality of light-receiving sections. When crosstalk from a light-receiving section for the 0th-order beam to light-receiving sections for the xc2x11st-order beams is xcex5 and crosstalk from the light-receiving sections for the xc2x11st-order beam to the light-receiving section for the 0th-order is xcex5xe2x80x2 in the light-receiving sections of the photodetector, quantity of light Q0 of the 0th-order light beam and quantity of light Qxc2x11 of the xc2x11st-order light beams has a relationship represented by a following equation:                                           Q            0                    ⁢                      :                    ⁢                      Q                          ±              1                                      =                                                            2                xc3x97                                  ϵ                  xe2x80x2                                            ϵ                                ⁢                      :                    ⁢          1.                                    (        1        )            
An integrated optical device according to the is invention comprises the light source for emitting a light beam, the diffraction grating for receiving the beam emitted from the light source and for generating three beams of 0th-order and xc2x11st-order light beams, and the photodetector which receives a beam and outputs a signal corresponding to a quantity of received light. The quantity of light Q0 of the 0th-order light beam and the quantity of light Qxc2x11 of the xc2x11st-order light beams has the above-mentioned relationship.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.
An advantage of the present invention is that it becomes possible to reduce the tracking error of the magnetic memory drive.